A working hypothesis of salt-ridge, salt-dome formation in the Louisiana Tertiary was formulated in 1957 to explain the observed phenomena along the Caillou Island, Timbalier Bay, Bay Marchand, West Delta Block 30, Venice, and Delta Duck trend: (1) regional down-to-the-north faults of very large stratigraphic throw on the southerly sectors of the domes; (2) a salt, deep-water facies shale ridge connecting Caillou Island, Timbalier Bay, and Bay Marchand at depth; (3) shallow occurrence of older deep-water shales beneath a condensed section on the upthrown sides of down-to-the-north faults; and (4) thick "normal" facies sections on the north flanks of the domes.

Application of results of seismic, bathymetric, and core data from the Gulf of Mexico continental slope gathered and interpreted by Lamont-Texas A&M and Shell groups shows that these phenomena are the results of wavelike salt ridge formation basinward from a prograding shelf edge due to differential loading.

Such ridges are present on the continental slope and the major down-to-the-north fault planes are postulated to coincide with the northern faces. The salt ridge grows asymmetrically in cross section, lifting the thinly covered upthrown block and allowing a thicker ponding of sediments on the landward downthrown block. Deep-water shales covering the early ridge roots join the diapiric action of the salt and are confined to the upthrown block until the salt breaks upward through the northward-dipping fault plane. As the salt is further buried by the prograding shelf sediments, it may leave the linear control of the fault and form individual domes with the commonly recognized pattern of shallow salt dome faulting and oil and gas accumulation.

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